A typical vane-type camshaft phaser generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil may be supplied to and from the camshaft phaser via a series of axial passages, and annular grooves cut on the inner diameter of the rotor. One groove is needed to supply oil to and from the advance chambers and one groove is needed to supply oil to and from the retard chambers. If the camshaft phaser includes an intermediate lock pin, an additional groove is needed to operate the intermediate lock pin. An additional groove is also needed if the camshaft phaser employs a centrally located oil control valve in order to supply oil thereto. Typically packaging more than two grooves in the rotor requires the rotor to be thicker than desired which undesirably increases the axial length of the camshaft phaser. Alternatively, packaging more that two grooves in the rotor without increasing the thickness of the rotor requires that the grooves be made narrower than desired which may lead to undesirable operation of the camshaft phaser, for example, slow operation thereof due to decreased oil flow capability. An additional factor that reduces the space available for the grooves in the rotor is that the camshaft is typically inserted axially into the rotor in order to locate the camshaft phaser coaxial with the camshaft. Another factor that reduces the space available for grooves in the rotor is that the camshaft phaser often includes a bias spring that extends axially into the rotor in order to bias the rotor into a default position when the internal combustion engine is not running.
German patent application publication number DE 10 2008 057 491 A1 discloses a camshaft phaser attached to a camshaft. The camshaft phaser includes a bushing between the rotor and camshaft phaser attachment bolt to partly define oil passages. However, the oil passages in the bushing require the bushing to be undesirably thick in order to accommodate both annular grooves and axial passages formed therein. Another drawback is that the bushing is clamped between the rotor and the camshaft and therefore must therefore be a part of the load path when transmitting camshaft torque.
What is needed is an axially compact camshaft phaser. What is also needed is such an axially compact camshaft phaser which does not compromise the size of oil passages used for communicating oil.